Sci­en­tist hits back at dam claims

Nelson Mail - - NEWS - CHERIE SIVIGNON

The Waimea River, near Nel­son, will be dry most sum­mers if more wa­ter is pumped from the aquifers un­der the plains with­out aug­men­ta­tion, ac­cord­ing to Land­care Re­search wa­ter sci­en­tist An­drew Fen­emor.

If min­i­mum flows in the river were to be main­tained and sea­wa­ter in­tru­sion avoided, there needed to be lim­its on wa­ter taken from the aquifers, he said.

Fen­emor is a for­mer Tas­man District Coun­cil en­vi­ron­men­tal man­ager and a mem­ber of the newly formed Com­mu­nity Wa­ter So­lu­tions Ad­vi­sory Group, set up to ad­vise the coun­cil and its pro­posed joint-ven­ture part­ner in the $82.5 mil­lion dam project, Waimea Ir­ri­ga­tors Ltd.

The dam is ear­marked for the Lee Val­ley and tipped to be funded by a mix of ratepayer, ir­ri­ga­tor and Crown fund­ing.

Fen­emor’s com­ments come in re­sponse to claims from a re­cently formed in­cor­po­rated so­ci­ety, Wa­ter In­for­ma­tion Net­work Inc (WIN), that there is ‘‘abun­dant’’ ca­pac­ity in the un­con­fined aquifer, from which most wa­ter is drawn for ur­ban and ru­ral use.

At a re­cent se­ries of pub­lic meet­ings, WIN sec­re­tary, re­searcher and for­mer Tas­man District Coun­cil can­di­date Mur­ray Daw­son ar­gued the aquifer had an ‘‘abun­dant safety mar­gin’’ of ‘‘re­serve wa­ter’’ down to sea level.

How­ever, Fen­emor said ‘‘re­serve wa­ter’’ was not ‘‘avail­able wa­ter’’.

‘‘If ‘re­serve wa­ter’ is used from the ex­ist­ing net­work of wells across the plains to meet pro­jected de­mand and se­cu­rity of sup­ply needs, the Waimea River will be dry most sum­mers,’’ he said. ‘‘Aquifer pump­ing has a big in­flu­ence in re­duc­ing river flows.’’

The un­con­fined aquifer and the river were ba­si­cally ‘‘one and the same’’, he said.

Un­der the aug­men­ta­tion pro­posal, wa­ter would be re­leased from the dam on a day-by-day ba­sis to main­tain the min­i­mum flow in the Waimea River and pro­vide suf­fi­cient wa­ter to main­tain high aquifer lev­els through­out sum­mer to meet daily pumped wa­ter de­mands.

‘‘Wa­ter re­leased from stor­age in­creases the wa­ter depth and width across the riverbeds and the slight in­crease in pres­sure be­tween river and un­der­ly­ing aquifer means there is in­creased leak­age to main­tain wa­ter stor­age in the aquifers through sum­mer,’’ Fen­emor said.

At the meet­ings, Daw­son also claimed salt­wa­ter in­tru­sion was a ‘‘red her­ring’’ and a ‘‘non is­sue’’.

Salt lev­els had never been above the Min­istry of Health guide­line, Daw­son said.

How­ever, Fen­emor said two bores on the coun­cil’s Waimea well­field were shut down per­ma­nently af­ter sea­wa­ter was drawn into them dur­ing a drought in 2001 ‘‘when pump­ing in­ter­cepted the salt­wa­ter wedge in the lower Waimea River’’.

The salt­wa­ter trig­ger was an elec­tri­cal con­duc­tiv­ity trig­ger in the Tas­man Re­source Man­age­ment Plan.

It was not re­lated to the drink­a­bil­ity of the wa­ter, Fen­emor said.

Daw­son pointed out that ir­ri­ga­tor pump­ing was not in­creas­ing and Fen­emor agreed, adding that was ex­pected ‘‘as there has been a mora­to­rium on new wa­ter takes since about 1996’’.

A main aim of the dam project was to pro­vide an ad­e­quate wa­ter sup­ply for all likely ur­ban and ru­ral de­mands for the next 100 years, he said.

The de­bate over the hy­drol­ogy be­hind the project has a long his­tory. Fen­emor was part of a 2016 peer re­view of the hy­dro­log­i­cal sci­ence un­der­pin­ning the de­sign and op­er­a­tion of the pro­posed dam that found it was ‘‘fit for pur­pose’’.

BRADEN FASTIER/STUFF

An­drew Fen­emor says the Waimea dam project aims to pro­vide ad­e­quate wa­ter sup­ply for ur­ban and ru­ral de­mands over the next 100 years.

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